Heat Range Facts

Autolite
®®
Technical Information
Spark Plug: Heat Range Facts
Typically, engines which are stock or are only slightly
modified, can use the original equipment (OE) recommended spark plug.
Racing Modified Engines – Generally, any engine
modification that alters the overall compression ratio
of the engine will involve spark plug selection issues.
One thing to consider is heat range.
• Cut Back Ground Electrode
• Anti-Corrosive Nickel Plating
• Large Yttrium Enhanced
Nickle Alloy Ground Electrode
for better heat transfer
The heat range of the spark plug determines how
much heat the spark plug is capable of removing
from the combustion chamber. The heat range of the
spark plug does not increase or decrease
horsepower. It changes the temperature of the tip of
the spark plug. If the heat range is too cold, the
deposits will not burn off the tip and the spark plug
will foul. If the spark plug heat range is too hot,
pre-ignition can occur.
A switch in heat range of the spark plug will change
the temperature of the spark plug tip by 70-120
degrees.
If you are unsure of the correct heat range to use,
always start with a colder spark plug. If the plug
is too cold, the plug will eventually foul and a
misfire will occur. This will not hurt the engine.
Unfortunately, though, if a spark plug that is too
hot is inadvertently chosen, pre-ignition and
detonation can severely damage your engine.
Don’t go to a hotter heat range unless you’ve
consulted your engine experts.
As there are many different ways to modify your
engine for racing applications, we can’t tell you here
which specific spark plug to use. If you have made
modifications to your engine, you should refer to your
component manufacturer’s specifications and/or
contact the experts at FRAM Group at
www.autolite.com.
FRAM Group IP LLC is not responsible for engine damage
resulting from improper spark plug selection due to
engine modifications or racing.
January 2012